Engines may use boosting devices, such as turbochargers, to increase engine power density. Thus, under steady state operation, smaller displacement turbocharged engines can produce power equivalent to larger displacement engines. However, under dynamic driving conditions, the smaller turbocharged engine may have less transient performance than a larger, naturally aspirated engine.
As one example, when a turbocharged engine is operating at low load, the turbocharger speed is low and intake manifold pressure is low. When the engine load is suddenly increased, there may be a lag before the turbocharger speed increases and intake manifold pressure rises. This delay may be referred to as “turbo-lag.” During this delay, the engine power or torque output may be less than the desired value, and less than the steady state available output.
One approach that attempted to provide intake manifold pressure boost with minimal delay is described in SAE paper 670109, published in 1967. This system used storage tanks to store compressed air with a carbureted, otherwise naturally aspirated gasoline engine. In this system, when the system was actuated, desired boost pressures were achieved rapidly.
Another approach is described in JP 59-99028. This system uses a compressed-air injecting port receiving air from a compressed-air tank, where the port was formed in a valve seat of the intake valve, and said port is opened when the intake valve is opened. An on-off valve is opened transiently for a prescribed period when an accelerator pedal is rapidly depressed. When the intake valve is open, air is injected through the valve seat for supplementing lack of air caused transiently when the accelerator pedal is depressed. Specifically, when the accelerator pedal depression signal exceeds a prescribed valve, the on-off valve is opened by a computer for a prescribed period corresponding to the pedal depressing speed. With such a system, boost compensation is allegedly unnecessary.
However, the inventors herein have recognized disadvantages with each of the above approaches. For example, if using the storage approach of SAE 670109, boost was provided for only a limited time since storage tanks were the only source of compressed air. Further, the system required two tanks of about 12 inches in diameter each, thus requiring significant packaging space in the vehicle.
When using a system such as JP 59-99028, while compressed air may be added to the engine, it does not appear that the energy of compression of the added air is used to amplify air flow through the main intake port. This means that the compressed air tank must be large enough to supply all of the desired increase of intake air mass.
In one approach, the above disadvantages may be overcome by a system for a vehicle traveling on the road. The system comprises: an engine having at least a cylinder with an intake valve configured to cover and uncover an intake opening into the cylinder, the cylinder coupled to an intake manifold; a compression device coupled to said engine; and an air delivery nozzle configured to deliver pressurized air to said cylinder via said opening, where said nozzle has a converging-diverging shape so that discharged air is at a supersonic velocity at least under some operating conditions. Further, in some embodiments, the discharged air may be mixed with a subsonic air stream, where the subsonic air stream is from the intake manifold
In this way, it is possible to take advantage of the compression device to enable reduced air storage, while utilizing a nozzle to more effectively utilize the compressed air that is available. For example, when the supersonic air stream is mixed with a subsonic stream from the intake manifold, the total momentum of the two streams is combined and conserved, so that the velocity of the mixed stream, and consequently the stagnation pressure, is increased. Thus, it is possible to use energy of the pressured air stream to increase the flow from the lower pressure intake manifold. In this way, less pressured air may be used to achieve desired compensation, thus improving efficiency in the use of the compressed air and in the storage space needed.